1. Field of the Invention
The present invention relates generally to a safety coupling arrangement, and particularly to a safety coupling arrangement that includes a first coupling part adaptable for a fixed co-action with a shaft, axle or corresponding element and which functions to transmit torque and rotational movement to the safety coupling, and a second coupling part adaptable for fixed co-action with a shaft, axle or corresponding element and which transmits torque and rotational movement from the safety coupling.
Safety couplings of this construction also include a safety unit which is adapted to take or be introduced into either one of two different setting positions, a first setting position in which torque and rotary movement can be transmitted between the two safety coupling parts, and a second setting position in which torque and rotary movement cannot be transmitted between the two safety coupling parts.
More particularly, the present invention is concerned with the use of a safety unit that can take the first setting position by virtue of an expansion of a hollow-cylindrical subpart or body, where the expansion is ensured by means of a pressure exerting agent or medium applied and enclosed in a cavity within the subpart of the safety unit, the pressure exerting agent or medium being illustrated hereinafter as an hydraulic pressure, such as an oil pressure, and that can take the second position by evacuating the pressure from the cavity.
A safety coupling according to the present invention is intended to find its application primarily in the transmissions by which there occurs sporadic torque stops, having, e.g., a duration of between 1 and 100 ms and expected to exceed a maximum torque for which such safety couplings are dimensioned.
Plants in which such conditions exist and utilise such rotatable transmissions are wind power, diesel motors and gas turbine motors driven by electric power generators, where frequent torque stops can occur in the event of short circuiting in the electric system or as a result of erroneous phasing (synchronisation) in respect of an electric power network.
More generally, a safety coupling according to the present invention, is adapted to enable it to transmit torque and rotary movement in an absence of slipping when the torque transmitted lies beneath a predetermined limit value, but causes activation of the safety unit immediately when this value is exceeded and a small relative movement occurs between the two safety coupling parts, the activated safety coupling quickly releasing the coupling action within the safety coupling such as to fully prevent any transmission of torque and rotational movement.
The present invention is based on a safety coupling as stated above wherein the material consumption in respect primarily of the second coupling part decreases successively in accordance with the chosen embodiment, without needing to relinquish the torque transfer requirement.
Described in the following is a safety coupling that includes a first externally-driven part, a second part that is driven by the safety coupling, and a safety unit which is normally integrated with the first coupling part. It should be noted, however, that the first coupling part and the second coupling part may switch places, without relinquishing the properties associated with the invention.
2. The Prior Art
Several different methods and arrangements of the aforesaid kind are known to the art.
The content of Swedish Patent Publication 78 06923-4, having a Publication No. 425 515, is a first example of known standpoint of techniques and the technical field to which the present invention relates.
This patent publication describes a safety coupling of the type which includes at least one thin-walled sleeve (12) that forms an axially directed defining wall in a generally ring-shaped chamber (15), wherewith the chamber is intended to receive a pressure fluid (17) with the intention of deforming the sleeve generally elastically in a radial direction, into clamping, locking engagement with a surface (21) of an element (11) intended for connection with the coupling (10), the shape and size of said surface corresponding generally to the surface (22) of said sleeve facing away from the chamber.
The publication makes particular reference to the fact that the chamber (15) includes an outlet (23) that is coordinated with an element (23, 30), which normally prevents the outflow of pressure fluid from the chamber but can be actuated to a state in which pressure fluid is allowed to leave the chamber and therewith actuate the coupling releasing state in response to a torsion or relative movement between each other and said surfaces (21, 22) on the coupling (10) and the element (11) respectively.
Another example of earlier standpoint of techniques is found in Swedish Patent Application 89 03077-9, having a Publication No. 463 327, said prior art document illustrating and describing a safety coupling for coupling together two co-axially rotatable parts (11, 12; 11′, 12′), e.g., a shaft and a hub, comprising a generally cylindrical coupling element (15), which is intended to be brought in between the parts that are to be coupled together and which is expandable both radially outwards and radially inwards so as to exert coupling pressure on said parts (11, 12; 11′, 12′) via the coupling element (15) and a possible insert (30, 31), wherein the coupling element accommodates a pressure chamber (16, 16′) which extends along said element and to which there is delivered a pressure fluid for achieving said expansion of the coupling element (15), and which includes means (25-27) for relieving said pressure in response to a relative rotation between said parts.
This prior art document describes a particular embodiment of the coupling element (15), in which said element exerts a greater coupling force on a first (11; 12′) of said parts than on a second (12; 11′) of said parts, wherein a pressure relieving means (25-27) is adapted to actuate a relative rotational movement between said first coupling part (11; 12′) and said coupling element (15) and therewith allow a rotation between said second coupling part (12; 11′) and said coupling element.
With regard to the special features of the present invention and the descriptions of these particular properties, it can be mentioned that FIG. 4 of said prior art Swedish patent publication 89 03077-9 shows and describes an arrangement that includes a plurality of components, where a subpart or a body, belonging to said safety unit, is inserted in a hollow-cylindrical groove whose width is adapted to correspond to a chosen small tolerated width or thickness of said subpart or body and where the groove is formed in a separate sleeve.
This embodiment illustrates that a coupling element (15) or a safety unit acts partly on a shaft (11) and partly on a hub (12) via an intermediate wall (30 and 31).
These form the illustrated legs of a single ring element (32) of “U”-shaped cross-section, wherein the ring element carries a shaft (11) via a bearing (19) together with the coupling (10).
The illustrated insert construction affords the advantage of avoiding the risk of damage to the coupling element (15) and the shaft (11) when releasing the coupling (10).
FIG. 4 also illustrates the use of a cylindrical gap (23) between said coupling element (15) and said hub (12).
In the case of safety couplings of this kind, it is usual to allow a coupling assembly to utilise three or more parts, of which one part is designed to surround a hollow-cylindrical subpart or body adapted for expansion and therewith serve as a force absorbing so-called holding-up means or counter-pressure means, for which it is dimensioned, wherein solely one cylindrical surface, the inner surface, of the hollow cylindrical body is adapted to create the desired torque transmission via pressure and friction.